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Abstract:

First output power is set in accordance with operation by a driver. In
addition, second output power greater than the first output power is set.
A hybrid vehicle is controlled so that an engine is driven in accordance
with the second output power. The hybrid vehicle is controlled so that
the engine is stopped when the first output power is equal to or smaller
than an engine stop threshold value.

Claims:

1-8. (canceled)

9. A control device for a hybrid vehicle which includes an internal
combustion engine, an electric motor, and a power storage device that
stores electric power to be supplied to said electric motor, and which
runs using at least one of said internal combustion engine and said
electric motor, comprising: means for setting first output power in
accordance with operation by a driver; means for setting second output
power greater than said first output power; means for controlling said
internal combustion engine to drive in accordance with said second output
power; means for stopping said internal combustion engine when said
second output power is equal to or smaller than a predetermined threshold
value in a first state; and stop means for stopping said internal
combustion engine when said first output power is equal to or smaller
than said threshold value in a second state different from said first
state.

10. The control device for a hybrid vehicle according to claim 9, wherein
said first state includes a state where a state of charge of said power
storage device is lower than a predetermined state of charge, and said
second state is a state that satisfies at least a condition that the
state of charge of said power storage device is equal to or higher than
said predetermined state of charge.

11. The control device for a hybrid vehicle according to claim 9, wherein
said first state includes a state where the temperature of coolant of
said internal combustion engine is lower than a predetermined
temperature, and said second state is a state that satisfies at least a
condition that the temperature of the coolant of said internal combustion
engine is equal to or higher than said predetermined temperature.

12. The control device for a hybrid vehicle according to claim 9, further
comprising means for setting, depending on the temperature of said power
storage device, an upper limit value of electric power discharged from
said power storage device, wherein said first state includes a state
where said upper limit value is smaller than a predetermined value, and
said second state is a state that satisfies at least a condition that
said upper limit value is equal to or greater than said predetermined
value.

13. The control device for a hybrid vehicle according to claim 9, wherein
said hybrid vehicle further includes an air conditioner for heating the
air in the vehicle interior by using coolant of said internal combustion
engine, said first state includes a state where said air conditioner is
operating to heat the air in said vehicle interior, and said second state
is a state that satisfies at least a condition that said air conditioner
is operating to cool the air in said vehicle interior, or a condition
that said air conditioner is in a stopped state.

14. A control method for a hybrid vehicle which includes an internal
combustion engine, an electric motor, and a power storage device that
stores electric power to be supplied to said electric motor, and which
runs using at least one of said internal combustion engine and said
electric motor, comprising the steps of: setting first output power in
accordance with operation by a driver; setting second output power
greater than said first output power; controlling said internal
combustion engine to drive in accordance with said second output power;
stopping said internal combustion engine when said second output power is
equal to or smaller than a predetermined threshold value in a first
state; and stopping said internal combustion engine when said first
output power is equal to or smaller than said threshold value in a second
state different from said first state.

15. A hybrid vehicle which includes an internal combustion engine, an
electric motor, and a power storage device that stores electric power to
be supplied to said electric motor, and which runs using at least one of
said internal combustion engine and said electric motor, comprising: an
operation unit operated by a driver; and a control unit that controls
said hybrid vehicle in accordance with operation on said operation unit
by the driver, wherein said control unit sets first output power in
accordance with the operation by the driver, sets second output power
greater than said first output power, controls said internal combustion
engine to drive in accordance with said second output power, stops said
internal combustion engine when said second output power is equal to or
smaller than a predetermined threshold value in a first state, and stops
said internal combustion engine when said first output power is equal to
or smaller than said threshold value in a second state different from
said first state.

Description:

TECHNICAL FIELD

[0001] The present invention relates to a control device for a hybrid
vehicle, a control method for a hybrid vehicle, and a hybrid vehicle, and
more particularly to a technique of controlling a hybrid vehicle so that
an internal combustion engine mounted thereon is stopped.

BACKGROUND ART

[0002] Hybrid vehicles incorporating an electric motor as a driving source
in addition to an internal combustion engine are known. In such hybrid
vehicle, when the vehicle speed is low, for example, the internal
combustion engine is stopped and only the electric motor can be used for
running. The internal combustion engine is started when the accelerator
position becomes larger, for example. It is desired to drive the internal
combustion engine with high thermal efficiency.

[0003] Japanese Patent Laying-Open No. 2006-94626 (PTL 1) discloses in
paragraph 0034 and the like that an engine is driven when requested power
that is set based on the accelerator position is equal to or greater than
a threshold value. Japanese Patent Laying-Open No. 2006-94626 also
discloses in paragraph 0036 and the like that the engine is operated
based on the requested power that is reset to increase by a compatible
value which is set to increase overall efficiency.

CITATION LIST

Patent Literature

[0004] PTL 1: Japanese Patent Laying-Open No. 2006-94626

SUMMARY OF INVENTION

Technical Problem

[0005] However, if requested power is set to increase after an internal
combustion engine has been started, it is difficult for the requested
power to become smaller than a threshold value used to determine whether
or not to stop the internal combustion engine. This may lower the
frequency with which the internal combustion engine is stopped and only
an electric motor is used for the running of a hybrid vehicle.

[0006] An object of the present invention is to increase the frequency
with which an internal combustion engine is stopped.

Solution to Problem

[0007] A control device for a hybrid vehicle which includes an internal
combustion engine, an electric motor, and a power storage device that
stores electric power to be supplied to the electric motor, and which
runs using at least one of the internal combustion engine and the
electric motor includes means for setting first output power in
accordance with operation by a driver, means for setting second output
power greater than the first output power, means for controlling the
internal combustion engine to drive in accordance with the second output
power, and stop means for stopping the internal combustion engine when
the first output power is equal to or smaller than a predetermined
threshold value.

[0008] A control method for a hybrid vehicle which includes an internal
combustion engine, an electric motor, and a power storage device that
stores electric power to be supplied to the electric motor, and which
runs using at least one of the internal combustion engine and the
electric motor includes the steps of setting first output power in
accordance with operation by a driver, setting second output power
greater than the first output power, controlling the internal combustion
engine to drive in accordance with the second output power, and stopping
the internal combustion engine when the first output power is equal to or
smaller than a predetermined threshold value.

[0009] A hybrid vehicle which includes an internal combustion engine, an
electric motor, and a power storage device that stores electric power to
be supplied to the electric motor, and which runs using at least one of
the internal combustion engine and the electric motor includes an
operation unit operated by a driver, and a control unit that controls the
hybrid vehicle in accordance with the operation on the operation unit by
the driver. The control unit sets first output power in accordance with
the operation by the driver, sets second output power greater than the
first output power, controls the internal combustion engine to drive in
accordance with the second output power, and stops the internal
combustion engine when the first output power is equal to or smaller than
a predetermined threshold value.

Advantageous Effects of Invention

[0010] When the first output power is equal to or smaller than the
predetermined threshold value, the hybrid vehicle is controlled so that
the internal combustion engine is stopped. The first output power is
smaller than the second output power. Thus, the first output power is
more likely than the second output power to become equal to or smaller
than the threshold value. Therefore, the frequency with which the
internal combustion engine is stopped is increased.

[0023] Embodiments of the present invention will be described below with
reference to the drawings. In the following description, the same parts
are denoted with the same reference numerals. Their designations and
functions are also the same. Therefore, a detailed description thereof
will not be repeated.

[0024] Referring to FIG. 1, a hybrid vehicle incorporates an engine 100, a
first motor generator 110, a second motor generator 120, a power split
device 130, a reduction gear 140, and a battery 150. Although a hybrid
vehicle that does not have a charge function from an external power
supply is described by way of example in the following description, a
plug-in hybrid vehicle that has a charge function from an external power
supply may be used.

[0025] Engine 100, first motor generator 110, second motor generator 120
and battery 150 are controlled by an ECU (Electronic Control Unit) 170.
ECU 170 may be divided into a plurality of ECUs.

[0026] This vehicle runs using a driving force from at least one of engine
100 and second motor generator 120. That is, either one or both of engine
100 and second motor generator 120 are automatically selected as a
driving source depending on the drive state.

[0027] For example, engine 100 and second motor generator 120 are
controlled in response to a result of operation on an accelerator pedal
172 by a driver. The amount of operation on accelerator pedal 172
(accelerator position) is detected by an accelerator position sensor (not
shown).

[0028] When the accelerator position is small and when the vehicle speed
is low, for example, the hybrid vehicle runs using only second motor
generator 120 as a driving source. In this case, engine 100 is stopped.
However, engine 100 may be driven for power generation, for example.

[0029] When the accelerator position is large, when the vehicle speed is
high, or when an SOC (State Of Charge) of battery 150 is low, for
example, engine 100 is driven. In this case, the hybrid vehicle runs
using only engine 100, or both of engine 100 and second motor generator
120, as a driving source.

[0030] Engine 100 is an internal combustion engine. An air-fuel mixture is
burned in a combustion chamber to rotate a crankshaft serving as an
output shaft. Exhaust gas emitted from engine 100 is cleaned by a
catalyst 102, and then emitted to the outside of the vehicle. Catalyst
102 performs a cleaning function when warmed up to a specific
temperature. Catalyst 102 is warmed up by heat of the exhaust gas.
Catalyst 102 is a three-way catalyst, for example.

[0031] Coolant of engine 100 circulates by passing through an air
conditioner 104 mounted on the hybrid vehicle. Air conditioner 104 heats
the air in the vehicle interior by using the coolant of engine 100. More
specifically, the coolant introduced into a heater core and the air
exchange heat, to deliver warmed air into the vehicle interior. A
well-known common technique can be utilized for air conditioner 104, and
thus a detailed description thereof will not be repeated.

[0032] Engine 100, first motor generator 110 and second motor generator
120 are connected via power split device 130. Motive power generated by
engine 100 is split into two paths by power split device 130. One of them
is a path for driving front wheels 160 via reduction gear 140. The other
is a path for driving first motor generator 110 to generate electric
power.

[0033] First motor generator 110 is a three-phase alternating current
rotating electric machine including a U-phase coil, a V-phase coil and a
W-phase coil. First motor generator 110 generates electric power using
motive power of engine 100 that is split by power split device 130. The
electric power generated by first motor generator 110 is used depending
on the running state of the vehicle or the SOC of battery 150. For
example, during normal running, electric power generated by first motor
generator 110 is directly used as electric power for driving second motor
generator 120. On the other hand, when the SOC of battery 150 is lower
than a predetermined value, electric power generated by first motor
generator 110 is converted from alternating current into direct current
by an inverter described later. Thereafter, the voltage is adjusted by a
converter described later, and stored in battery 150.

[0034] When first motor generator 110 acts as a power generator, first
motor generator 110 generates negative torque. The negative torque as
used herein refers to such torque that becomes a load on engine 100. When
first motor generator 110 receives power supply and acts as a motor,
first motor generator 110 generates positive torque. The positive torque
as used herein refers to such torque that does not become a load on
engine 100, that is, such torque that assists in rotation of engine 100.
This is applicable to second motor generator 120.

[0035] Second motor generator 120 is a three-phase alternating current
rotating electric machine including a U-phase coil, a V-phase coil and a
W-phase coil. Second motor generator 120 is driven by at least one of
electric power stored in battery 150 and electric power generated by
first motor generator 110.

[0036] The driving force from second motor generator 120 is transmitted to
front wheels 160 via reduction gear 140. Accordingly, second motor
generator 120 assists engine 100, or allows the vehicle to run with the
driving force from second motor generator 120. The rear wheels may be
driven instead of or in addition to front wheels 160.

[0037] During regenerative braking of the hybrid vehicle, second motor
generator 120 is driven by front wheels 160 via reduction gear 140,
causing second motor generator 120 to operate as a power generator.
Accordingly, second motor generator 120 operates as a regenerative brake
for converting braking energy into electric power. The electric power
generated by second motor generator 120 is stored in battery 150.

[0038] Power split device 130 is formed of a planetary gear including a
sun gear, pinion gears, a carrier, and a ring gear. The pinion gears are
engaged with the sun gear and ring gear. The carrier supports the pinion
gears so that they are rotatable on their own axes. The sun gear is
coupled to the rotation shaft of first motor generator 110. The carrier
is coupled to the crankshaft of engine 100. The ring gear is coupled to
the rotation shaft of second motor generator 120 and reduction gear 140.

[0039] Since engine 100, first motor generator 110 and second motor
generator 120 are coupled via power split device 130 formed of the
planetary gear, the rotational speeds of engine 100, first motor
generator 110 and second motor generator 120 have the relation
represented by a straight line in an alignment chart.

[0040] Battery 150 is a battery pack configured so that a plurality of
battery modules, each formed by integrating a plurality of battery cells,
are connected in series. Battery 150 has a voltage of about 200 V, for
example. Battery 150 is charged with electric power supplied from first
motor generator 110 and second motor generator 120, as well as from a
power supply outside of the vehicle. A capacitor may be used instead of
or in addition to battery 150.

[0041] Referring to FIG. 2, an electrical system of the hybrid vehicle is
further described. The hybrid vehicle includes a converter 200, a first
inverter 210, a second inverter 220, and a system main relay 230.

[0042] Converter 200 includes a reactor, two npn transistors, and two
diodes. The reactor has one end connected to the positive electrode side
of each battery, and the other end connected to a node between the two
npn transistors.

[0043] The two npn transistors are connected in series. The npn
transistors are controlled by ECU 170. A diode is connected between the
collector and the emitter of each npn transistor to allow current to flow
from the emitter side to the collector side.

[0044] As the npn transistor, an IGBT (Insulated Gate Bipolar Transistor)
can be used, for example. Instead of the npn transistor, a power
switching element such as a power MOSFET (Metal Oxide Semiconductor
Field-Effect Transistor) can be used.

[0045] When electric power discharged from battery 150 is supplied to
first motor generator 110 or second motor generator 120, the voltage is
boosted by converter 200. Conversely, when electric power generated by
first motor generator 110 or second motor generator 120 is charged to
battery 150, the voltage is decreased by converter 200.

[0046] A system voltage VH between converter 200 and each inverter is
detected by a voltage sensor 180. The detection result from voltage
sensor 180 is sent to ECU 170.

[0047] First inverter 210 includes a U-phase arm, a V-phase arm and a
W-phase arm. The U-phase arm, V-phase arm and W-phase arm are connected
in parallel. The U-phase arm, V-phase arm and W-phase arm each have two
npn transistors connected in series. A diode is connected between the
collector and the emitter of each npn transistor to allow current to flow
from the emitter side to the collector side. Then, the node between the
npn transistors in each arm is connected to an end different from a
neutral point 112 of each coil of first motor generator 110.

[0048] First inverter 210 converts direct current supplied from battery
150 into alternating current, and supplies the alternating current to
first motor generator 110. First inverter 210 also converts alternating
current generated by first motor generator 110 into direct current.

[0049] Second inverter 220 includes a U-phase arm, a V-phase arm and a
W-phase arm. The U-phase arm, V-phase arm and W-phase arm are connected
in parallel. The U-phase arm, V-phase arm and W-phase arm each have two
npn transistors connected in series. A diode is connected between the
collector and the emitter of each npn transistor to allow current to flow
from the emitter side to the collector side. Then, the node between the
npn transistors in each arm is connected to an end different from a
neutral point 122 of each coil of second motor generator 120.

[0050] Second inverter 220 converts direct current supplied from battery
150 into alternating current, and supplies the alternating current to
second motor generator 120. Second inverter 220 also converts alternating
current generated by second motor generator 120 into direct current.

[0051] Converter 200, first inverter 210 and second inverter 220 are
controlled by ECU 170.

[0052] System main relay 230 is provided between battery 150 and converter
200. System main relay 230 is a relay for switching between a state in
which battery 150 and the electrical system are connected and a state in
which they are cut off. When system main relay 230 is in an opened state,
battery 150 is cut off from the electrical system. When system main relay
230 is in a closed state, battery 150 is connected to the electrical
system.

[0053] The state of system main relay 230 is controlled by ECU 170. For
example, when ECU 170 is activated, system main relay 230 is closed. When
ECU 170 is stopped, system main relay 230 is opened.

[0054] Referring to FIG. 3, a manner in which engine 100 is controlled is
further described. As shown in FIG. 3, when output power of the hybrid
vehicle is smaller than an engine start threshold value, the hybrid
vehicle runs using only the driving force from second motor generator
120.

[0055] The output power is set as power used for running of the hybrid
vehicle. The output power is calculated by ECU 170 in accordance with a
map having the accelerator position, vehicle speed and the like as
parameters, for example. It is noted that the way to calculate the output
power is not limited thereto. It is noted that torque, acceleration,
driving force, accelerator position or the like may be used instead of
the output power.

[0056] When the output power of the hybrid vehicle becomes equal to or
greater than the engine start threshold value, engine 100 is driven.
Accordingly, the hybrid vehicle runs using the driving force from engine
100 in addition to or instead of the driving force from second motor
generator 120. In addition, electric power generated by first motor
generator 110 using the driving force from engine 100 is directly
supplied to second motor generator 120.

[0057] As shown in FIG. 4, an operating point of engine 100, namely, an
engine speed NE and output torque TE are determined by a point of
intersection of the output power and an operating line.

[0058] The output power is represented by equal-power lines. The operating
line is predetermined by a developer based on the results of experiments
and simulations. The operating line is set so that engine 100 can be
driven with optimal (highest) fuel economy. That is, the optimal fuel
economy is achieved by driving engine 100 along the operating line. It is
noted that in a range between a predetermined torque TE1 and a
predetermined torque TE2, the operating line is set so that vibration and
noise are reduced. It is noted that the way to set the operating line is
not limited thereto.

[0059] When the point of intersection of the output power and the
operating line is in the range between predetermined torque TE1 and
predetermined torque TE2 as shown in FIG. 5, the optimal fuel economy is
not achieved. In view of this, to achieve the optimal fuel economy, the
output power is corrected to increase when driving engine 100, as shown
in FIG. 6. Specifically, the output power is increased to achieve the
optimal fuel economy.

[0060] As a result, as shown in FIG. 7, after engine 100 is started at
time T1, the hybrid vehicle is controlled to attain second output power
P2 corrected to increase, instead of first output power P1 set based on
the accelerator position. For example, the hybrid vehicle is controlled
so that the output power of engine 100 is second output power P2.

[0061] The difference between first output power P1 requested by the
driver and second output power P2 is used, for example, to generate
electric power using first motor generator 110 to charge battery 150.

[0062] After engine 100 is started, when the output power becomes equal to
or smaller than an engine stop threshold value, engine 100 is stopped.
Thus, the hybrid vehicle runs using only the driving force from second
motor generator 120. For example, the hybrid vehicle is controlled so
that the output power of second motor generator 120 is first output power
P1. The engine stop threshold value is set to be smaller than the engine
start threshold value by the developer in consideration of hysteresis.

[0063] Whether to compare first output power P1 set based on the
accelerator position with the engine stop threshold value, or to compare
second output power P2 corrected to increase with the engine stop
threshold value is switched depending on the drive state of the hybrid
vehicle.

[0064] Referring to FIG. 8, the function of ECU 170 in this embodiment is
described. The function described below may be implemented by hardware,
software, or cooperation of hardware and software.

[0065] ECU 170 includes a first setting unit 301, a second setting unit
302, a controlling unit 304, a limiting unit 306, a first stopping unit
311, and a second stopping unit 312.

[0066] First setting unit 301 sets the first output power in accordance
with operation on accelerator pedal 172 by the driver. For example, the
first output power is set in accordance with a map having the accelerator
position, vehicle speed and the like as parameters.

[0067] Second setting unit 302 sets second output power P2 greater than
first output power P1. Second output power P2 is set so that engine 100
is driven at an operating point where the optimal fuel economy is
achieved.

[0068] Controlling unit 304 controls engine 100 to drive in accordance
with second output power P2. For example, the hybrid vehicle is
controlled so that the output power of engine 100 is second output power
P2.

[0069] Controlling unit 306 sets, depending on the temperature of battery
150, an upper limit value WOUT of electric power discharged from battery
150. For example, upper limit value WOUT is set depending on the
temperature of battery 150, based on a map shown in FIG. 9. It is noted
that the way to set upper limit value WOUT of electric power discharged
from battery 150 is not limited thereto. The electric power discharged
from battery 150 is limited to be equal to or smaller than upper limit
value WOUT.

[0070] Referring back to FIG. 8, when second output power P2 is equal to
or smaller than the predetermined engine stop threshold value in a first
state, first stopping unit 311 controls the hybrid vehicle so that engine
100 is stopped.

[0071] When first output power P1 is equal to or smaller than the engine
threshold value in a second state different from the first state, second
stopping unit 312 controls the hybrid vehicle so that engine 100 is
stopped.

[0072] The first state includes a state where the SOC of battery 150 is
lower than a predetermined SOC, a state where the temperature of the
coolant of engine 100 is lower than a predetermined temperature, a state
where upper limit value WOUT of electric power discharged from battery
150 is smaller than a predetermined value, and a state where air
conditioner 104 is operating to heat the air in the vehicle interior.

[0073] Therefore, in a state where the SOC of battery 150 is lower than a
predetermined SOC, a state where the temperature of the coolant of engine
100 is lower than a predetermined temperature, a state where upper limit
value WOUT of electric power discharged from battery 150 is smaller than
a predetermined value, or a state where air conditioner 104 is operating
to heat the air in the vehicle interior, when second output power P2 is
equal to or smaller than the predetermined engine stop threshold value,
the hybrid vehicle is controlled so that engine 100 is stopped.

[0074] The second state is a state other than the first state. Thus, the
second state satisfies at least a condition that the SOC of battery 150
is equal to or higher than the predetermined SOC. More specifically, the
second state is a state where the SOC of battery 150 is equal to or
higher than the predetermined SOC, the temperature of the coolant of
engine 100 is equal to or higher than the predetermined temperature,
upper limit value WOUT of electric power discharged from battery 150 is
equal to or greater than the predetermined value, and air conditioner 104
is operating to cool the air in the vehicle interior, or is in a stopped
state.

[0075] Therefore, in a state that satisfies all of the conditions that the
SOC of battery 150 is equal to or higher than the predetermined SOC, the
temperature of the coolant of engine 100 is equal to or higher than the
predetermined temperature, upper limit value WOUT of electric power
discharged from battery 150 is equal to or greater than the predetermined
value, and air conditioner 104 is operating to cool the air in the
vehicle interior, or is in a stopped state, when first output power P1 is
equal to or smaller than the engine threshold value, the hybrid vehicle
is controlled so that engine 100 is stopped.

[0076] The first and second states are not limited to these states. For
example, the first state may be a state where the SOC of battery 150 is
lower than the predetermined SOC, and the second state may be a state
where the SOC of battery 150 is equal to or higher than the predetermined
SOC.

[0077] The state where the SOC of battery 150 is lower than the
predetermined SOC is a state where, in short, electric power that can be
discharged from battery 150 is smaller than a prescribed value, and
electric power that can be charged to battery 150 is greater than a
prescribed value.

[0078] The state where the temperature of the coolant of engine 100 is
equal to or lower than the predetermined temperature is a state where, in
short, engine 100 needs to be warmed up.

[0079] Referring to FIG. 10, a control configuration of the hybrid vehicle
is described.

[0080] In step (hereinafter abbreviated as S) 100, ECU 170 sets first
output power P1 in accordance with operation on accelerator pedal 172 by
the driver. Namely, first output power P1 is set in accordance with the
accelerator position.

[0081] In S102, ECU 170 determines whether or not first output power P1 is
equal to or greater than the engine start threshold value. If first
output power P1 is equal to or greater than the engine start threshold
value (YES in S102), the process proceeds to S104. If not (NO in S102),
the process proceeds to S108.

[0082] In S104, ECU 170 sets second output power P2 greater than first
output power P1.

[0083] In S106, ECU 170 controls the hybrid vehicle so that engine 100 is
driven in accordance with second output power P2.

[0084] In S108, ECU 170 controls the hybrid vehicle so that engine 100 is
stopped and only second motor generator 120 is used as a driving source
for running. For example, the hybrid vehicle is controlled so that the
output power of second motor generator 120 is first output power P1.

[0085] In S110, ECU 170 determines whether or not the drive state of the
vehicle is the first state. If the drive state of the vehicle is the
first state (YES in S110), the process proceeds to S112. If the drive
state of the vehicle is the second state (NO in S110), the process
proceeds to S114.

[0086] In S112, ECU 170 determines whether or not second output power P2
is equal to or smaller than the engine stop threshold value. If second
output power P2 is equal to or smaller than the engine stop threshold
value (YES in S112), the process proceeds to S116. If not (NO in S112),
the process returns to S104.

[0087] In S114, ECU 170 determines whether or not first output power P1 is
equal to or smaller than the engine stop threshold value. If first output
power P1 is equal to or smaller than the engine stop threshold value (YES
in S114), the process proceeds to S116. If not (NO in S114), the process
returns to S104.

[0088] In S116, ECU 170 stops engine 100.

[0089] As described above, according to the hybrid vehicle in this
embodiment, engine 100 is controlled to be driven in accordance with
second output power P2 greater than first output power P1 set in
accordance with the operation on accelerator pedal 172 by the driver.
When first output power P1 is equal to or smaller than the engine stop
threshold value in the second state, engine 100 is stopped. First output
power P1 is smaller than second output power P2. Thus, first output power
P1 is more likely than second output power P2 to become equal to or
smaller than the engine start threshold value. Therefore, the frequency
with which engine 100 is stopped is increased.

Other Embodiments

[0090] As shown in FIG. 11, the present invention can also be applied to a
hybrid vehicle incorporating only a motor generator 122 mainly used as a
driving source, and not including a motor generator mainly used as a
power generator.

[0091] As shown in FIG. 12, the present invention can also be applied to a
series-type hybrid vehicle in which engine 100 is used only to drive
first motor generator 110, and second motor generator 120 is always used
for running.

[0092] It should be understood that the embodiments disclosed herein are
illustrative and non-restrictive in every respect. The scope of the
present invention is defined by the terms of the claims, rather than the
description above, and is intended to include any modifications within
the scope and meaning equivalent to the terms of the claims.